This invention relates to an electrophotographic photoreceptor and, particularly, to a novel electrophotographic photoreceptor having a photosensitive layer containing an azo pigment. More particularly, it relates to a highly durable electrophotographic photoreceptor high in sensitivity and suitable for repeated use.
Hitherto, there have been widely known those having a photosensitive layer mainly composed of inorganic photoconductive materials such as selenium, zinc oxide and cadmium sulfide.
However, these photoreceptors are not necessarily satisfactory in sensitivity, thermal stability, moisture resistance and durability. Especially, the toxicity of selenium and cadmium sulfide imposes some restriction on their manufacture and handling.
On the other hand, recently, electrophotographic photoreceptors having a photosensitive layer mainly composed of an organic photoconductive compound have attracted much attention because of the ease of their manufacture and thermal stability superior to the selenium photoreceptors.
A well known organic photoconductive compound is poly-N-vinylcarbazole. However, an electrophotographic photoreceptor having a photosensitive layer mainly composed of a charge transfer complex formed from the poly-N-vinylcarbazole and a Lewis acid such as 2,4,7-trinitro-9-fluorenone is not necessarily satisfactory in sensitivity and durability.
Photoreceptors of functionally separated type such as a laminated type and a dispersion type, in which the carrier generating function and the carrier transfer function are respectively borne by different substances have advantages that the materials can be selected from a wide range and thus electrophotographic photoreceptors having any of characteristics such as charge characteristic, sensitivity and durability can be relatively easily produced.
Hitherto, various carrier generating materials and carrier transfer materials have been proposed.
For example, electrophotographic receptors have been put to practical use which has a photosensitive layer comprising a combination of a carrier generating layer comprising amorphous selenium and a carrier transfer layer mainly composed of poly-N-vinylcarbazole. However, the carrier generating layer comprising amorphous selenium is inferior in durability.
Furthermore, use of organic dyes and pigments as a carrier generating material has been proposed and, for example, electrophotographic photoreceptors containing monoazo pigment or bisazo pigment in the photosensitive layer are disclosed in Japanese Patent Kokoku No. 48-30513, Japanese Patent Kokai Nos. 52-4241 and 54-46558 and Japanese Patent Kokoku No. 56-11945. However, these azo pigments are not completely satisfactory in sensitivity, residual potential and stability in repeated use and besides, scope of selection of carrier transfer materials is limited. Thus, the fact is that there are no electrophotographic photoreceptors which fully meet a wide variety of requirements of the electrophotographic process.